1. Field of the Invention
The present invention relates to the technical field of gas turbines. It concerns a method for operating a gas turbine, as well as a gas turbine system for carrying out the method.
2. Brief Description of the Related Art
Usually burners such as the so-called EV burner (double cone burner, ref., for example, U.S. Pat. No. 5,081,844) and the so-called SEV burner (secondary EV burner, ref., for example, an article by F. Joos et al. Development of the sequential combustion system for the GT24/GT26 gas turbine family, ABB Review 4, p. 4-16 (1998) or U.S. Pat. No. 5,454,220) used in gas turbines are designed for full load operation. Nonetheless it might be necessary to operate the gas turbine at partial load. This might be because the network cannot absorb the generated energy or the gas turbine is started up or shut down (repairs, etc.). If no special measures are taken, partial load operation results in an unfavorable emission behavior with regard to CO and NOx. Another problem with partial load operation of a gas turbine concerns the residue of the relatively cool exhaust gas in relatively short combustion chambers. Cold gases and short dwell times result in low NOx emissions, but unfortunately also in increased CO/UHC emissions.
Publication U.S. Pat. No. 5,081,844 mentioned in the introduction proposes addressing the issue of emissions with partial loads by alternating the arrangement of small and large premix burners and having the small premix burners function as pilot burners. Publication U.S. Pat. No. 5,454,220 mentioned in the introduction proposes this procedure for gas turbines with SEV burners.
The disadvantage with this kind of emissions optimization for partial load operation is the fact that the burners in the main combustion chamber must be specially configured in order to allow for the corresponding operation. This procedure is difficult to realize in retrospect in existing gas turbines without any special burner arrangement, and thus it is difficult to eliminate emissions issues during partial load operation.